Effects of hydrogen peroxide-generating systems on the Wolff-Chaikoff effect.

In bovine thyroid slices, the inhibition of organic binding of iodide by excess iodide in the range 5-10 micrograms/ml was prevented by incubating the slices in the presence of TSH. The Wolff-Chaikoff effect was also overcome by the presence of a hydrogen peroxide-generating system, such as glucose-glucose-oxidase or tyramine. TSH and hydrogen peroxide enhanced the synthesis of both iodotyrosines and iodothyronines. The enhanced organification of iodine in the presence of TSH or hydrogen peroxide was not due to an abrupt synthesis of organic iodine during the early phase of incubation before intrathyroidal iodide concentrations had reached the inhibitory levels. These findings suggest that the inhibition of organic binding of iodine in the presence of excess iodide may be due to a diminished generation or a decreased availability of hydrogen peroxide in the thyroid.